Exemplary embodiments relate to a nonvolatile memory device and a method of programming the same and, more particularly, to a nonvolatile memory device and a method of programming the same, which are capable of reducing the time for performing a program operation.
Semiconductor memory devices may be classified into random access memory (RAM) devices, such as dynamic random access memory (DRAM) and static random access memory (SRAM) which are volatile (i.e., data stored in the memory devices are lost after a lapse of a certain time) and are fast in a rate of data input and output, and nonvolatile memory devices which retain data once the data are stored therein.
In the nonvolatile memory devices, there has been an increasing demand for flash memory devices which enable the electrical input and output of data. The flash memory device can be electrically erased at high speed even without removing a circuit from a board. The flash memory device is advantageous in that it does not require the refresh function of retaining data and it has a low manufacturing cost per memory because the structure of a memory cell is simple.
The flash memory devices are typically classified into a NOR type and a NAND type. The NOR type flash memory is disadvantageous in terms of high integration because it requires one contact for two cells, but is advantageous in terms of high speed because it has a high cell current. The NAND type flash memory is disadvantageous in terms of high speed because it has a low cell current, but is advantageous in terms of high integration because a plurality of cells shares one contact. Accordingly, the NAND type flash memory devices have been in the spot-light as the next-generation memory devices with a rapid increase in the use of digital devices, such as MP3 players, digital cameras, mobile terminals, and auxiliary storage devices.
Recently, to further increase the degree of integration of the flash memory devices, active research is being carried out on a multi-bit cell capable of storing plural data in a single memory cell. This type of a memory cell is called a multi-level cell (MLC). A memory cell capable of storing a single bit is called a single level cell (SLC).
The MLC has been developed to store data of 2 bits, and an MLC capable of storing data of 4 bits or 8 bits is being developed. In the flash memory devices, distributions of the threshold voltages are subdivided with an increase in the number of bits. In general, the performance of the flash memory device may be better as the width of a distribution of the threshold voltages becomes narrower.
In general, in an MLC capable of storing data of 2 bits, when a program operation is performed, a least significant bit (LSB) data program operation is first performed and a most significant bit (MSB) data program operation is then performed. Furthermore, in an MLC capable of storing data of 4 bits or more (e.g., 8 bits or 16 bits), the number of program operations is increased in proportion to the number of bits. Accordingly, an MLC capable of storing many pieces of data is disadvantageous in that the time for performing a program operation is increased.